Powertrain lash management

ABSTRACT

Methods and systems are provided for adjusting powertrain torque in a vehicle based on driver intent. Driver intent is inferred based on foot motion inside a foot well monitored via a foot well region sensor and changes in clearance outside the vehicle monitored via a range sensor. By adjusting powertrain torque based on operator foot motion and traffic movements outside the vehicle, frequency of lash transitions can be reduced and lash transition initiation can be adjusted based on expected changes in torque demand.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 15/210,631, entitled “POWERTRAIN LASH MANAGEMENT,” filed onJul. 14, 2016. The entire contents of the above-referenced applicationare hereby incorporated by reference in its entirety for all purposes.

FIELD

The present description relates generally to methods and systems forcontrolling a vehicle engine to manage lash in a vehicle driveline.

BACKGROUND/SUMMARY

Lash in a vehicle may occur due to lost motion caused by slack orclearance within components of a vehicle driveline. Driveline torquetransitions through zero torque during powertrain braking or propulsionmay create clunk or backlash in the driveline causing driver discomfort.By gently taking up lash before substantial torque is applied, effectsof crossing the lash zone may be mitigated to reduce driver discomfortand improve vehicle drivability. Several approaches of managing lash ina vehicle transmission system have been studied.

On example approach of managing driveline lash is provided by Yamazakiet al. in U.S. Pat. No. 8,954,215. Therein, a controller controls torquefrom a traction motor coupled to an engine and driveline input torque tovehicle wheels during torque reversal from positive to negative torquein order to limit the rate of change of traction and driveline torque.In another example, shown by Stroh in U.S. Pat. No. 7,171,299, a rate oftorque change in a vehicle driveline may be reduced to threshold levelsby a system with a torque based module, a filter and an engine controlmodule. The torque based module generates a torque request based onoperator input. The filter, whose parameters are determined based onengine operating conditions, modifies the torque request by reducingtorque changes to a predetermined torque range. The engine controlmodule receives the modified torque request and controls engine throttleand spark timing to improve engine efficiency and minimize emissions.

However, the inventors herein have recognized potential issues relatingto such methods of managing lash in a vehicle driveline. Specifically,lack of lead information on a driver intent (such as whether the driverwill eventually brake or accelerate) to guide adjustments in drivelinetorque may create slow vehicle response and reduce vehicle drivability.For example, a driveline torque may be adjusted during an acceleratorpedal tip-out assuming that the operator is going to apply the brakepedal. However, if the operator does not apply the brake pedal butcoasts and then reapplies the accelerator pedal, then the drivelinetorque may unnecessarily transition through the lash zone multipletimes. As a result, repeated lash adjustments may slow down vehicleresponse and also create additional driver discomfort.

Thus in one example, some of these issues may be at least partlyaddressed by a method for a vehicle engine, comprising: in response toan operator foot-off pedal event, distinguishing between a driver intentto brake or coast based on one or more of operator foot motion insidethe vehicle and traffic patterns outside the vehicle; and varying lashadjustments during torque transition through a lash region following theoperator foot-off accelerator pedal event based on the driver intent. Inthis way, torque adjustments may be selected that better manage movementthrough a lash region based on an upcoming torque transition.

As one example, responsive to a foot-off accelerator pedal event, acontroller may initiate powertrain braking to reduce torque. Inaddition, the controller may infer and distinguish a driver intent tobrake from a driver intent to coast based on the output of a camerainside a vehicle foot-well area, the output from a traffic sensor,operator drive history, etc. Based on the inferred driver intent, lashadjustments for the driveline may be varied. For example, based on adriver foot motion towards a brake pedal and/or in response tosignificant traffic ahead of the vehicle following the foot-offaccelerator pedal event, the controller may infer that the driver islikely to brake and may adjust the lash in the vehicle driveline byproviding a slight negative torque (since substantial negative torque isexpected thereafter during the braking event). In addition, thecontroller may initiate a transition through the lash region to a creeptorque later. As another example, based on driver foot remaining nearthe accelerator brake pedal and/or traffic clearing in front of thevehicle following the accelerator foot-off pedal event, the controllermay infer that the driver is likely to coast and may maintain a slightpositive torque in the driveline (since substantial positive torque isexpected thereafter during the coasting event) and may not transitionthrough the lash region unless the operator applies the brake pedal.Alternatively, the controller may initiate a transition through the lashregion to a creep torque earlier.

The approach described here may confer several advantages. For example,the method allows driveline torque adjustments to be made in a timelymanner to improve vehicle response and improve drivability. By usingoutput from the foot camera and traffic sensor to determine if theoperator intends to brake or coast, the expected torque profilefollowing a foot-off pedal event may be better predicted, allowing forlash adjustments to be accordingly performed. By adjusting the amountand rate of powertrain braking torque applied following the foot-offpedal event based on the predicted torque profile, torque transitionsthrough the lash zone may be conducted with improved efficiency. Bymaintaining a slight positive torque in the driveline when the driver isanticipated to coast, frequent transitions through the lash region arereduced, providing fuel economy and NVH benefits. Consequently, vehicleresponse during lash adjustments may be improved, improving vehicledrivability, and minimizing torque variations. By improving lashadjustments, driveline component life may be extended.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents an engine with a transmission and various components.

FIG. 2 shows a schematic depiction of a combustion chamber of an enginesystem.

FIG. 3 represents a flowchart for adjusting torque in a vehicledriveline.

FIG. 4 depicts a flowchart for processing information from a foot camerainside a vehicle and traffic patterns outside the vehicle, to be used inconjunction with FIG. 3.

FIG. 5 shows example graphical output for adjusting lash in a vehicledriveline based on foot motion and traffic movements outside thevehicle.

DETAILED DESCRIPTION

The following description relates to systems and methods for managinglash in a vehicle driveline coupled to an engine system, such as theengine system of FIG. 2 in the vehicle system of FIG. 1. The approachprovides an improved method for adjusting driveline torque based onoperator foot motion captured by a foot camera inside a vehicle, andtraffic patterns captured by a camera looking outside the vehicle. Acontroller may be configured to perform a control routine, such as theexample routine of FIG. 3 to adjust torque in a vehicle driveline basedon driver intent. The controller may infer driver intent based onoperator foot motion captured by a foot camera inside a vehicle andtraffic movements outside the vehicle, as described with reference toFIG. 4. FIG. 5 shows an example graphical output for driveline lashadjustments in a vehicle based on predicted driver intent. By utilizingthe systems and methods described herein, the technical effect ofadjusting lash in a vehicle driveline based on operator foot motioninside the foot well and traffic movements outside the vehicle to keeptorque variations within allowable thresholds, may be achieved.

FIG. 1 shows a block diagram of a vehicle drive-train 100. Drive-train100 may be powered by engine 10. In one example, engine 10 may be agasoline engine. In alternate examples, other engine configurations maybe employed, for example, a diesel engine. Engine 10 may be started withan engine starting system (not shown). Further, engine 10 may generateor adjust torque via torque actuator 104, such as a fuel injector,throttle, etc.

An engine output torque may be transmitted to torque converter 106 todrive an automatic transmission 108 by engaging one or more gearclutches (to engage gears), including forward clutch 110, where thetorque converter may be referred to as a component of the transmission.Further, the gear clutches including forward clutch 110 may be needed toactivate a plurality of fixed transmission gear ratios. As such,automatic transmissions may engage several clutches to transmit power tothe wheels. However, for purposes of simplification, in the presentdescription, any such combinations may be referred to as engaging aforward clutch. Torque converter 106 includes an impeller 120 thattransmits torque to turbine 122 via hydraulic fluid. One or moreclutches may be engaged to change mechanical advantage between theengine vehicle wheels 114. Impeller speed may be determined via speedsensor 125, and turbine speed may be determined from speed sensor 126 orfrom vehicle speed sensor 130. The output of the torque converter may inturn be controlled by torque converter lock-up clutch 112. As such, whentorque converter lock-up clutch 112 is fully disengaged, torqueconverter 106 transmits torque to automatic transmission 108 via fluidtransfer between the torque converter turbine and torque converterimpeller, thereby enabling torque multiplication. In contrast, whentorque converter lock-up clutch 112 is fully engaged, the engine outputtorque is directly transferred via the torque converter clutch to aninput shaft (not shown) of transmission 108. Alternatively, the torqueconverter lock-up clutch 112 may be partially engaged, thereby enablingthe amount of torque relayed to the transmission to be adjusted. Acontroller 12 may be configured to adjust the amount of torquetransmitted by the torque converter by adjusting the torque converterlock-up clutch in response to various engine operating conditions, orbased on a driver-based engine operation request. Fluid within theautomatic transmission may be pressurized via a mechanical pump (notshown) driven via the engine. In some examples, the automatictransmission further includes a one-way clutch (not shown) that allowsthe engine to provide torque to the automatic transmission and wheels,but does not allow the wheels to supply torque to the engine.

Torque output from the automatic transmission 108 may in turn be relayedto wheels 114 to propel the vehicle. Specifically, automatictransmission 108 may adjust an input driving torque at the input shaft(not shown) responsive to a vehicle traveling condition beforetransmitting an output driving torque to the wheels.

Further, wheels 114 may be locked by engaging wheel brakes 116. In oneexample, wheel brakes 116 may be engaged in response to the driverpressing his foot on a brake pedal (not shown). In the similar way,wheels 114 may be unlocked by disengaging wheel brakes 116 in responseto the driver releasing his foot from the brake pedal.

During conditions when the engine torque (or driveline torque) changesdirection, such as when going from positive to negative torque, or whengoing from negative to positive torque, lash may occur. This may becaused due to lost motion caused by slack or clearance within variousdriveline components when torque changes direction, such as during avehicle acceleration or deceleration event. In addition, motion ofpowertrain mounts may be functionally similar to powertrain lash whereinthe lash-like property of the mounts may be dynamically altered viaadjustments to mount stiffness. Frequent transitions through a lashregion (defined by a torque region on either side of zero torque) canresult in NVH issues and disturbance to the vehicle driver.

Responsive to a foot-off an accelerator pedal, a controller may initiatepowertrain braking to reduce the drivetrain torque to a decelerationtorque level. In an effort to limit wheel brake wear and improve fueleconomy, the kinetic energy of the vehicle may be harvested duringconditions when a vehicle operator removes their foot from anaccelerator pedal. The harvested kinetic energy can then be used to idlethe engine idle without fuel (that is, provide a DFSO condition), andpower an accessory drive, such as an alternator, an AC compressor, avacuum pump, a transmission hydraulic pump, etc. The engine controllermay transition between negative and positive powertrain torque slowlyenough to minimize vehicle occupant disturbance but fast enough so thatthe fuel economy benefits are not lost. As elaborated herein, by betteranticipating driver intent and traffic requirements, an enginecontroller may reduce a frequency of torque transitions, as well asbetter infer lead information on the occurrence of an upcoming torquetransition.

The controller may select between providing powertrain braking as a wayof conserving brake wear (or being independent of wheel brake control)and providing powertrain braking in an effort to turn the accessorydrive or idle the engine with little or no fuel. For example, powertrainbraking may be provided via a powertrain deceleration approach withfueling enabled wherein engine air flow rate is minimized by closing anintake throttle and optionally minimizing air trapping via valve timingadjustments. At the same time, engine fueling may be adjusted based onthe airflow to maintain an air-fuel ratio at or around stoichiometry. Atransmission coupled to the engine may be held in-gear (such as with aforward clutch engaged) and with a torque converter locked so that thetorque converter can efficiently transmit negative torque. Thecontroller may then command the transmission into a gear wherein thespeed ratio enables the engine to be run at or near an idle speed (or atan engine speed higher than idle speed if higher levels of powertraindeceleration are desired). The controller may also engage an ACcompressor clutch to raise an AC pressure and thus its stored energy. Assuch, this increases the AC load on the engine. The controller may alsoincrease an alternator field (or increase alternator output) to maximizethe energy storage rate (assuming that the battery has additionalstorage capacity).

As an alternate example, powertrain braking may be provided via apowertrain deceleration approach with fueling disabled wherein thetransmission is held in gear and the torque converter is locked whilefueling is disabled. As with the fuel-on approach, one or more engineloads, such as the AC compressor load and the alternator load, on theengine may be increased. As such, the fuel-off approach may improve thefuel economy while increasing the powertrain braking if it reducesfriction braking compared to the fuel-on powertrain decelerationapproach.

In particular, powertrain braking is used to reduce the drivetraintorque to a level outside a lash region of the powertrain, the rate ofreducing based on the displacement of the accelerator pedal during thefoot-off pedal event. Then, further powertrain braking is appliedalongside lash adjustments to transition through the lash region duringa positive-to-negative torque reversal. The powertrain torque is thenreduced to a deceleration torque level (slight negative torque), fromwhere the torque is then increased to a creep torque level (slightpositive torque) via another transition through the lash region during anegative-to-positive torque reversal Initiation of the lash transitionto the creep torque level is adjusted based on the driver intent, withthe initiation performed earlier when the driver intends to coast, andthe initiation performed later when the driver intends to brake.

In one example, lash adjustments during torque reversals may be made bycoupling the engine to drive wheels in such a way as to let the enginetransmit both positive and negative torque. Subsequently, the engineintake throttle may start to be closed. The intake throttle may beclosed at a faster rate until the desired torque point (which may be thezero torque point) is approached. A slower throttle motion may beapplied prior to reaching the desired torque point or zero torque inorder to reduce the rate of torque change in that region. Once thetorque transition is complete, increased negative torque may be appliedat a higher rate of change.

A mechanical oil pump (not shown) may be in fluid communication withautomatic transmission 108 to provide hydraulic pressure to engagevarious clutches, such as forward clutch 110 and/or torque converterlock-up clutch 112. The mechanical oil pump may be operated inaccordance with torque converter 106, and may be driven by the rotationof the engine or transmission input shaft, for example. Thus, thehydraulic pressure or flow rate generated in mechanical oil pump mayincrease as an engine speed increases, and may decrease as an enginespeed decreases.

Referring to FIG. 2, a schematic diagram showing one cylinder of amulti-cylinder engine 10 in an engine system 200, which may be includedin a propulsion system, such as in vehicle 201. In one example, enginesystem 200 may be included in vehicle drive-train 100 of FIG. 1.

The engine 10 may be controlled at least partially by a control systemincluding a controller 12 and by inputs from a vehicle operator via afirst input device 270 and a second input device 276. In this example,the first input device 270 includes an accelerator pedal (herein alsoreferred to as a go pedal) and a first pedal position sensor 274 forgenerating a proportional accelerator pedal position signal. The secondinput device 276 includes a brake pedal and a second pedal positionsensor 278 for generating a proportional brake pedal position signal.

Vehicle 201 may include one or more sensors for providing situationalawareness. As an example, a foot-well sensor, for example configured asa foot camera 280, located inside a vehicle foot-well region, may scanthe foot-well region and monitor motion of operator's foot in thefoot-well region, in particular, the motion of the operator's foot inthe vicinity of each of the accelerator pedal and brake pedal, and relaya motion signal to controller 12. For example, the sensor may provideinformation regarding a position of the operator's foot relative to eachof the accelerator pedal and the brake pedal during pedal tip-in andtip-out events, as well as immediately before and after such events.

The controller may also receive input from a range sensor 290 configuredto provide a distance to objects in the path of vehicle 201. Rangesensor 290 may be RADAR, light detecting and ranging (LiDAR), sonar, orother known distance ranging device. In one example, range sensor 290may be configured as a traffic camera for scanning a region ahead of/infront of vehicle 201. For example, the sensor 290 may provide inputregarding a closing rate of vehicle 201 (a time taken for vehicle 201 toclose into a vehicle immediately ahead of it), a clearance ahead of thevehicle, etc.

Still other situational awareness sensors may include, for example,global positioning systems (GPS), radio receivers, etc.

A combustion chamber 230 of the engine 10 may include a cylinder formedby cylinder walls 232 with a piston 236 positioned therein. The piston236 may be coupled to a crankshaft 240 so that reciprocating motion ofthe piston is translated into rotational motion of the crankshaft. Thecrankshaft 240 may be coupled to at least one drive wheel of a vehiclevia an intermediate transmission system. Further, a starter motor may becoupled to the crankshaft 240 via a flywheel to enable a startingoperation of the engine 10.

The combustion chamber 230 may receive intake air from an intakemanifold 244 via an intake passage 242 and may exhaust combustion gasesvia an exhaust passage 248 to an exhaust treatment device 250. Theintake manifold 244 and the exhaust passage 248 can selectivelycommunicate with the combustion chamber 230 via respective intake valve252 and exhaust valve 254. In some examples, the combustion chamber 230may include two or more intake valves and/or two or more exhaust valves.

In this example, the intake valve 252 and exhaust valve 254 may becontrolled by cam actuation via respective cam actuation systems 251 and253. The cam actuation systems 251 and 253 may each include one or morecams and may utilize one or more of cam profile switching (CPS),variable cam timing (VCT), variable valve timing (VVT), and/or variablevalve lift (VVL) systems that may be operated by the controller 12 tovary valve operation. The position of the intake valve 252 and exhaustvalve 254 may be determined by position sensors 255 and 257,respectively. In alternative examples, the intake valve 252 and/orexhaust valve 254 may be controlled by electric valve actuation. Forexample, the cylinder 230 may alternatively include an intake valvecontrolled via electric valve actuation and an exhaust valve controlledvia cam actuation including CPS and/or VCT systems.

A fuel injector 266 is shown coupled directly to combustion chamber 230for injecting fuel directly therein in proportion to the pulse width ofa signal received from the controller 12. In this manner, the fuelinjector 266 provides what is known as direct injection of fuel into thecombustion chamber 230. The fuel injector may be mounted in the side ofthe combustion chamber or in the top of the combustion chamber, forexample. Fuel may be delivered to the fuel injector 266 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail. In someexamples, the combustion chamber 230 may alternatively or additionallyinclude a fuel injector arranged in the intake manifold 244 in aconfiguration that provides what is known as port injection of fuel intothe intake port upstream of the combustion chamber 230.

Spark is provided to combustion chamber 230 via spark plug 292. Theignition system may further comprise an ignition coil (not shown) forincreasing voltage supplied to spark plug 266. In other examples, suchas a diesel, spark plug 266 may be omitted.

The intake passage 242 may include a throttle 262 having a throttleplate 264. In this particular example, the position of throttle plate264 may be varied by the controller 12 via a signal provided to anelectric motor or actuator included with the throttle 262, aconfiguration that is commonly referred to as electronic throttlecontrol (ETC). In this manner, the throttle 262 may be operated to varythe intake air provided to the combustion chamber 230 among other enginecylinders. The position of the throttle plate 264 may be provided to thecontroller 12 by a throttle position signal. The intake passage 242 mayinclude a mass air flow sensor 220 and a manifold air pressure sensor222 for sensing an amount of air entering engine 10.

The controller 12 is shown in FIG. 2 as a microcomputer, including amicroprocessor unit 202, input/output ports 204, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 206 (e.g., non-transitory memory) in this particularexample, random access memory 208, keep alive memory 210, and a databus. The controller 12 may receive various signals from sensors coupledto the engine 10, in addition to those signals previously discussed,including measurement of inducted mass air flow (MAF) from the mass airflow sensor 220; engine coolant temperature (ECT) from a temperaturesensor 212 coupled to a cooling sleeve 214; an engine position signalfrom a Hall effect sensor 218 (or other type) sensing a position ofcrankshaft 240; throttle position from a throttle position sensor 265;manifold absolute pressure (MAP) signal from the sensor 222; acceleratorsignal from the first pedal sensor 274; brake signal from the secondpedal sensor 278; inside vehicle motion signal from camera 280, andoutside vehicle motion signal from range sensor 290. An engine speedsignal may be generated by the controller 12 from crankshaft positionsensor 218. Manifold pressure signal also provides an indication ofvacuum, or pressure, in the intake manifold 244. Note that variouscombinations of the above sensors may be used, such as a MAF sensorwithout a MAP sensor, or vice versa. During engine operation, enginetorque may be inferred from the output of MAP sensor 222 and enginespeed. Further, the MAP sensor, along with the detected engine speed,may be a basis for estimating charge (including air) inducted into thecylinder. In one example, the crankshaft position sensor 218, which isalso used as an engine speed sensor, may produce a predetermined numberof equally spaced pulses every revolution of the crankshaft.

In still further examples, vehicle 201 may include a Global positioningsystem (GPS) receiver receiving satellite positioning data via radiosignals transmitted by a satellite. The GPS receiver may receivepositioning data that may be used to index maps to determine trafficpatterns or signals, road grade, and other road features such asdistance to leading vehicle. Further still, a radio receiver receivingradio signals from a stationary transmitter may be used to learn trafficpatterns (such as based on locations of traffic accidents and backups).In another example, information on traffic patterns or signals, roadgrade, and other road features such as distance to leading vehicle maybe gleaned from vehicle-to-vehicle data broadcasting and receivingsystems.

The storage medium read-only memory 206 can be programmed with computerreadable data representing non-transitory instructions executable by theprocessor 202 for performing the methods described below as well asother variants that are anticipated but not specifically listed.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 254 closes and intake valve 252 opens. Airis introduced into combustion chamber 230 via intake manifold 244, andpiston 236 moves to the bottom of the cylinder so as to increase thevolume within combustion chamber 230. The position at which piston 236is near the bottom of the cylinder and at the end of its stroke (e.g.,when combustion chamber 230 is at its largest volume) is typicallyreferred to by those of skill in the art as bottom dead center (BDC).

During the compression stroke, intake valve 252 and exhaust valve 254are closed. Piston 236 moves toward the cylinder head so as to compressthe air within combustion chamber 230. The point at which piston 236 isat the end of its stroke and closest to the cylinder head (e.g., whencombustion chamber 230 is at its smallest volume) is typically referredto by those of skill in the art as top dead center (TDC). In a processhereinafter referred to as injection, fuel is introduced into thecombustion chamber. In a process hereinafter referred to as ignition,the injected fuel is ignited by known ignition means such as spark plug292, resulting in combustion.

During the expansion stroke, the expanding gases push piston 236 back toBDC. Crankshaft 240 converts piston movement into a rotational torque ofthe rotary shaft. Finally, during the exhaust stroke, the exhaust valve254 opens to release the combusted air-fuel mixture to exhaust manifold248 and the piston returns to TDC. Note that the above is shown merelyas an example, and that intake and exhaust valve opening and/or closingtimings may vary, such as to provide positive or negative valve overlap,late intake valve closing, or various other examples.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine, and each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

As will be appreciated by someone skilled in the art, the specificroutines described below in the flowcharts may represent one or more ofany number of processing strategies such as event driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various acts or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Like, the order ofprocessing is not necessarily required to achieve the features andadvantages, but is provided for ease of illustration and description.Although not explicitly illustrated, one or more of the illustrated actsor functions may be repeatedly performed depending on the particularstrategy being used. Further, these Figures graphically represent codeto be programmed into the computer readable storage medium in controller12 to be carried out by the controller in combination with the enginehardware, as illustrated in FIG. 2.

Based on input from one or more of the above-mentioned sensors,controller 12 may adjust one or more actuators, such as fuel injector266, throttle 262, spark plug 292, intake/exhaust valves and cams, etc.The controller may receive input data from the various sensors, processthe input data, and trigger the actuators in response to the processedinput data based on instruction or code programmed therein correspondingto one or more routines. For example, in response to receiving a footmotion signal from camera 280, the controller may adjust drivelinetorque in a vehicle in order to reduce torque variations. In oneexample, based on a driver moving foot towards a brake pedal following afoot-off pedal event, it may be inferred that the driver intends tobrake. A controller may be adjusted to provide a slight negative torque,since substantial negative torque may be expected thereafter. Examplecontrol routines will be described later with regard to FIGS. 3-4.

In this way, the system of FIGS. 1-2 enables a vehicle systemcomprising: an operator foot-well region including an accelerator pedal,a brake pedal, and a foot-well sensor; a sensor coupled to the vehiclesystem for estimating a gap between the vehicle system and a leadingvehicle; an engine including a fuel injector and an intake throttlevalve; and a controller. The controller may be configured withcomputer-readable instructions stored on non-transitory memory for: inresponse to a foot-off accelerator pedal event, applying a firstpowertrain brake torque to reduce engine torque to a threshold torqueabove a lash region via adjustments to a duty cycle of the fuel injectorand an opening of the intake throttle valve; inferring a driver intentto coast or brake based on one or more of the traffic sensor and thefoot-well sensor; and selectively performing a lash adjustment throughthe lash region based on the inferred driver intent. As an example, theselectively performing the lash adjustment includes: performing the lashadjustment when the inferred driver intent includes braking; and notperforming the lash adjustment when the inferred driver intent includescoasting. The selectively performing the lash adjustment furtherincludes: initiating the lash adjustment through the lash region earlierwhen the inferred driver intent includes coasting; and initiating thelash adjustment through the lash region later when the inferred driverintent includes braking.

In another example, lash adjustments during engine torque reversals maybe made when an engine is coupled to drive wheels such that the enginetransmits both positive and negative torque. Subsequently, an engineactuator (such as an engine intake throttle) may be adjusted to reducethe rate of torque change during torque transitions from positive tonegative or torque changes from negative to positive (e.g., at a slowerthan a threshold rate of torque change). Thereafter, the engine actuatormay be adjusted to increase the rate of torque change (e.g., at higherthan the threshold rate of torque change). Referring to FIG. 3, anexample method 300 is shown for adjusting powertrain torque based ondriver intent as inferred from driver foot motion inside a foot-well andtraffic movements outside the vehicle. Instructions for carrying outmethod 300 and the rest of the methods included herein may be executedby a controller based on instructions stored on a memory of thecontroller and in conjunction with signals received from sensors of theengine system, such as the sensors described above with reference toFIGS. 1-2. The controller may employ engine actuators of the enginesystem to adjust engine operation, according to the methods describedbelow.

At 302, method 300 includes estimating and/or measuring vehicle andengine operating conditions. Operating conditions may include but arenot limited to driver torque demand, electrical load, mass air flow,manifold absolute pressure, engine speed, engine load, accelerator pedalposition, brake pedal position, throttle position, vehicle speed, enginetemperature, and vehicle clearance (that is, a gap between the givenvehicle and a leading vehicle immediately ahead of the given vehicle, asdetermined based on traffic movements outside the given vehicle). Afterdetermining vehicle operating conditions, method 300 proceeds to 304.

At 304, method 300 may include adjusting engine settings based on torquedemand. For example, throttle opening, cylinder fueling, torqueconverter slip settings, boost pressure settings, etc., may be adjustedbased on torque demand. In particular, the controller may operate theengine combusting air and fuel to provide a demanded torque. Thedemanded torque may include a driver demanded torque as determined fromaccelerator pedal position, and the demanded torque may also includetorque to keep the engine at or above idle speed and torque (e.g., creeptorque) to move the vehicle at a low speed when the driver is notapplying the accelerator pedal. Further, the vehicle's transmission maybe shifted to neutral while the engine idles (e.g., neutral idle).

Next at 306, the routine may monitor operator foot position and trafficmovements outside the vehicle while the vehicle is being operated. Assuch, the monitoring may be performed during the entirety of the vehicledrive cycle. Operator foot position may be monitored based on input froma sensor or camera scanning a foot-well region of the vehicle. Trafficmovements outside the vehicle may be determined based on input from asensor or camera scanning a region in front of the given vehicle.Monitoring operator foot position may include monitoring the motion ofthe operator foot relative to each of the accelerator pedal and thebrake pedal. For example, it may be determined if the operator isapplying or releasing the accelerator pedal or the brake pedal, if theoperator is hovering over one of the pedals, if the operator's foot ismoving from pedal to the other pedal, etc. Further, during anyaccelerator or brake pedal events, a rate of pedal displacement (duringboth applying and releasing of the pedal), as well as angle of pedalapplication/release may be monitored. Further still, the controller maylearn an operator's driving pattern (or update a learned pattern storedin the controller's memory) based on a frequency of pedal application, asequence of pedal application, durations elapsed betweenapplication/release of one pedal and release/application of the otherpedal, intervals between successive applications of the same pedal, etc.For example, based on the rate, frequency, sequence, and intervals ofpedal application, the controller may infer if the operator has adriving preference for performance or for fuel economy. As elaboratedherein at FIG. 4, based on the driver's foot motion, the controller mayinfer and distinguish a driver intent to coast from a driver intent tobrake.

Monitoring traffic movements and traffic patterns may includedetermining a number of vehicles within a defined radius of the givenvehicle (e.g., vehicles ahead and to the side of the given vehicle), anddetermining a gap or clearance between the given vehicle and a leadingvehicle (e.g., a distance from the front bumper of the given vehiclefrom a rear bumper of a vehicle immediately ahead of it), as well as aclosing speed (speed to close in to leading vehicle). Monitoring trafficpatterns may further include determining if traffic outside the vehicleis slowing down (e.g., if the gap/clearance to the leading vehicle isdecreasing) or clearing up (e.g., if the gap/clearance to the leadingvehicle is increasing). Further still, the monitoring of trafficpatterns may be used to determine road conditions, such as road grade(e.g., whether an uphill or a downhill segment is approaching). Aselaborated herein at FIG. 4, based on the traffic pattern, thecontroller may infer and distinguish a driver intent to coast from adriver intent to brake.

Next at 308, it may be determined if a foot-off go pedal event hasoccurred. In one example, a foot-off go pedal event may be confirmed ifan accelerator pedal tip-out event is detected by a pedal positionsensor based on the release of the accelerator pedal. As anotherexample, a foot-off go pedal event may be confirmed based on theposition of a driver's foot with respect to the accelerator pedal, asdetermined by a sensor/camera in the foot-well region. If a foot-off gopedal event is not confirmed, at 312, the method includes maintainingengine settings, and then the routine exits.

To improve drive cycle fuel economy, when a driver releases anaccelerator pedal, a controller may decelerate the driveline torque to anegative torque. For example, the vehicle may be decelerated viadriveline or powertrain braking at a constant or consistent rate untilthe driver request torque for acceleration, or until the vehicle speedis at zero speed or within a threshold of zero speed. This providesseveral advantages. First, a fuel cut-off responsive to the foot-off gopedal reduces fuel usage. Then, the engine is idled using energy thatwould otherwise have gone into brake heat. Also, a front end accessorydrive (FEAD) system may be powered using energy that would haveotherwise gone into brake heat. Further, the application of adeceleration torque to a slightly negative torque level upon operatorfoot-off the accelerator pedal allows for the vehicle to slow downquicker.

Thus, by using at least some of the vehicle's kinetic energy to recoverat least a fraction of the energy improves fuel economy by reducing theenergy loss to friction braking. Thus, even if the unintended powertrainbraking which tends to occur at foot-off-accelerator is not conducive tofuel economy, the fuel economy gains achieved via the minimization ofpowertrain torque reversals outweighs any fuel economy loss incurred dueto the powertrain braking.

When the driver wants to slow down the vehicle, they may take their footoff the accelerator pedal. As a result, a fixed level of deceleration isachieved, the fixed level resulting from road load, aerodynamic (drag)loads, and powertrain braking. The pedal itself may not be easilycontrollable between a given level of powertrain braking and zeropowertrain braking. Consequently, more powertrain braking may occur thanwas desired. As elaborated herein, if the operator foot remains near thego pedal or the inferred state of the traffic indicates that significantdeceleration is not likely to be desired, it may be advantageous tocircumvent the transition to powertrain braking which would include atransition from positive to negative torque (and a likely return topositive torque). As such, the move to the slightly negativedeceleration torque level requires a transition through the lash regionof the drivetrain (which is defined by a band of torque on either sideof zero torque), and a corresponding lash adjustment. As such, this maybe a first lash adjustment performed during a positive-to-negativetorque reversal. In addition, after reaching the slight negativedeceleration torque level, the powertrain is held in neutral idle for awhile before powertrain torque is increased to a slight positive creeptorque level via second lash adjustment during negative-to-positivetorque reversal. Not only do the lash transitions result in NVH issues,but the lash adjustments can impact the fuel economy gains made earlier.The inventors herein have recognized that a controller may decide howmuch driveline braking to apply and whether to and when to put thedriveline torque into a state with slightly negative torque, slightlypositive torque, or neutral, following the foot-off accelerator pedalevent based on the driver's subsequent intent. In particular, if animminent driver brake command is anticipated, then it may beadvantageous to provide more driveline brake torque and transitionthrough the lash region to get to the slightly negative decelerationtorque level as quickly as possible, and then transition through thelash region to get to the creep torque level later. In one example,creep torque may be reached at vehicle speeds less than 10 kilometersper hour when a vehicle with an unlocked torque converter travels on aflat road. However, if an imminent driver brake command is notanticipated, or if an imminent driver positive torque command isanticipated, then it may be advantageous to coast by maintaining aslightly positive driveline torque (or be in neutral or idle) whilestaying outside the lash region rather than commanding powertrainbraking. In this case, lash transitions are not performed, and aninstantaneous smooth acceleration can be performed when the driverdemands a torque increase, improving drivability. Alternatively, it maybe advantageous to provide less driveline brake torque and transitionthrough the lash region to get to the slightly negative decelerationtorque level slowly, and then transition through the lash region to getto the creep torque level earlier. In other words, lash adjustmentsduring torque transitions through a lash region following an operatorfoot-off pedal event may be varied based on the driver intent.

Thus, if the foot-off accelerator pedal event is confirmed, the routineproceeds to 310, wherein the controller may infer and distinguishbetween the driver intent to brake or coast (responsive to the foot-offaccelerator pedal event) based on one or more or each of the monitoringof the operator foot position and the traffic patterns. As an example, adriver intent to brake may be inferred based on the driver moving theirfoot towards (or hovering around) the brake pedal following the foot-offgo pedal event and/or traffic slowing down outside the vehicle (or adecrease in vehicle closing/clearance) following the foot-offaccelerator pedal event. A negative driveline torque may be expectedduring such conditions. As another example, a driver intent to coast maybe inferred based on the driver hovering their foot over or around theaccelerator pedal following the foot-off go pedal event and/or based ontraffic clearing outside the vehicle (or an increase in vehicleclosing/clearance). A positive driveline torque may be expected duringsuch conditions. Distinguishing between driver intent to brake or coastmay further include, as non-limiting examples, indicating driver intentto brake responsive to operator foot motion towards a brake pedal andindicating driver intent to coast responsive to operator foot motionnear an accelerator pedal. The operator foot motion inside the vehiclemay be based on input from a camera scanning a foot-well region of thevehicle. As another example, distinguishing between driver intent tobrake or coast may include indicating driver intent to brake responsiveto a traffic pattern indicative of a smaller clearance (or closing rate)ahead of the vehicle and indicating driver intent to coast responsive toa traffic pattern indicative of a larger clearance (or closing rate)ahead of the vehicle. The traffic pattern and clearance outside thevehicle may be based on input from a camera scanning a region in frontof, or ahead of, the vehicle. The details of inferring driver intentbased on operator foot motion inside the vehicle and traffic patternsoutside the vehicle are discussed in detail at FIG. 4.

After inferring the driver intent, at 314, the routine may determine ifvehicle slowing via light powertrain braking is required. In oneexample, an intent to slow the vehicle down via light powertrain brakingmay be inferred if the driver moves their foot towards the brake pedalor if the closing rate/clearance between the given vehicle and thevehicle in front decreases (such as when traffic ahead of the givenvehicle slows down). If the answer is YES, the routine proceeds to 315wherein the controller may adjust one or more engine actuators toprovide a powertrain braking level that provides a target decelerationrate while taking advantage of fuel economy resulting from using thevehicle's stored kinetic energy to idle the engine and power the FEAD.Herein, the light powertrain braking is applied before a brake pedal isactually applied and may include a less than threshold amount ofpowertrain braking applied to decelerate the vehicle at a slower rate.In comparison, the powertrain braking applied when the brake pedal isactually applied may be higher than the threshold amount and maydecelerate the vehicle at a faster rate.

As an example, the controller may reduce engine torque via powertrainbraking to a threshold torque level outside a lash region of thedriveline, and then transition through the lash region via a first lashadjustment (during a positive to negative torque transition through thelash region) to reach a deceleration torque level. A rate of powertrainbraking to the threshold torque level as well as a timing of the firstlash adjustment may be adjusted based on a rate of pedal displacementduring the operator foot-off accelerator pedal event. For example, ifthe pedal is displaced at a higher rate (e.g., a higher closing rate ofthe pedal), then a higher rate of powertrain braking (and/or higheramount of powertrain braking) may be applied and the first lashadjustment may be performed earlier.

It will be appreciated that the powertrain braking applied and thetiming of the first lash adjustment may be further based on a learnedoperator driving pattern, the operator driving pattern including apreference for performance or a preference for fuel economy. As anexample, based on a frequency, order, sequence, interval, and degree ofapplication of each of the accelerator pedal and the brake pedal by theoperator, the controller may learn a driving pattern. For example, thecontroller may learn if the operator has a lead foot, if they brake hardand often, if they prefer to coast, etc. In one example, when theoperator driving pattern reflects a preference for fuel economy (overperformance), the amount and rate of driveline braking applied followingthe foot-off accelerator pedal may be smaller such that the vehicledecelerates to the deceleration torque level slower, and the first lashadjustment occurs later during the torque transition. In comparison,when the operator driving pattern reflects a preference for performance(over fuel economy), the amount and rate of driveline braking appliedfollowing the foot-off accelerator pedal may be larger such that thevehicle decelerates to the deceleration torque level faster, and thefirst lash adjustment occurs earlier during the torque transition.

Torque modulation during the lash crossing may be achieved via one ormore engine load end-effectors. For example, an engine throttle or anair intake valve timing may be adjusted to modulate torque during torquereversals. In another example, spark timing may be retarded, andaccessory engine loads may be increased to quickly reduce torque duringtorque transitions through the lash zone. Applying the powertrainbraking responsive to the foot-off accelerator pedal event includesswitching off fuel to the engine cylinders, and shifting thetransmission into gear with the torque converter locked while the enginespins unfueled. Optionally, one or more engine loads may also beincreased to enable a higher driveline braking and to enable the firstlash adjustment to be performed earlier. For example, an air conditionercompressor load and/or an alternator load on the engine may beincreased. Further still, driveline braking torque may be increased byadjusting the engine valve timing to increase pumping losses. Thepowertrain torque may then be held at the deceleration torque levelbefore driveline torque is increased to a creep torque level following asecond lash adjustment during a negative to positive transition throughthe lash region. As elaborated below, a timing of the second lashadjustment may be varied based on whether and how soon an increase intorque demand is expected, as based on the driver intent.

Next at 317, method 300 may determine if negative torque is expected inthe driveline. That is, it is determined if there is an indication thatthe driver may brake. The determination may be based on the monitoredoperator foot motion inside the foot-well region and/or based on trafficpatterns ahead of the vehicle. In one example, negative torque isexpected responsive to the driver moving their foot towards the brakepedal (or hovering over the brake pedal), and/or traffic slowing downoutside the vehicle resulting in a larger closing rate or smallerclearance between the given vehicle and a leading vehicle. Details ofdetermining expected negative torque based on driver foot motion andtraffic movements outside the vehicle are discussed at FIG. 4. Ifnegative powertrain torque is expected, the routine proceeds to 318.

At 318, in response to the driver intent to brake, the controllerperforms the second lash adjustment by moving through the lash regionlater before maintaining creep torque. Herein, when the driver intentincludes braking, a duration between the first lash adjustment and thesecond lash adjustment is larger, and the powertrain torque is held atthe slight negative deceleration torque level longer. By transitioningthrough the lash zone later when negative driveline torque may beexpected, engine may be prepared to quickly convert vehicle kineticenergy to idle and FEAD power, keeping torque variations to allowablelevels while improving fuel economy and vehicle response. In addition,additional negative driveline torque can be provided while the drivelineis already at the deceleration torque level, obviating the need for thesecond lash adjustment. By reducing frequent lash region transitions,fuel economy is improved and NVH issues are reduced.

If negative driveline torque is not expected the routine proceeds to320. In one example, negative driveline torque is not expected when thedriver moves their foot away from the brake pedal (or hovers over theaccelerator pedal), and/or traffic clears up outside the vehicleresulting in a smaller closing rate or larger clearance between thegiven vehicle and the leading vehicle. Herein, it is inferred that thedriver is likely to imminently increase torque demand.

At 320, in response to the expected positive driveline torque, thecontroller performs the second lash adjustment by moving through thelash region earlier before maintaining creep torque. Herein, when thedriver intent does not include braking, the duration between the firstlash adjustment and the second lash adjustment is smaller, and thepowertrain torque is held at the slight negative deceleration torquelevel for a shorter amount of time. Further, the creep torque level isattained earlier. By transitioning through the lash zone earlier whennegative driveline torque is not expected, driveline torque variationsmay be kept within threshold levels while improving vehicle response andreducing driver discomfort. In addition, when positive driveline torqueis demanded, the demanded torque can be rapidly provided while thedriveline is already at the creep torque level. As such, this improvesdrivability and reduces time to torque.

Returning to 314, if it is determined that vehicle slowdown usingpowertrain braking is not requested, at 316, it may be determined if thedriver intends to slow the vehicle down via coasting. In one example, anintent to slow the vehicle down via coasting may be inferred if thedriver moves their foot away from the brake pedal, hovers their footover the accelerator pedal, or if the closing rate/clearance between thegiven vehicle and the vehicle in front increases (such as when trafficahead of the given vehicle clears up). If the answer is YES, the routineproceeds to 322. Otherwise, the routine returns to 306 to monitoroperator foot position and traffic movements outside the vehicle duringthe drive cycle. Next at 322, powertrain braking may be adjusted tomaintain slight positive or creep torque. In particular, the controllermay adjust one or more engine actuators to provide a powertrain brakinglevel that decelerates vehicle and reduces the powertrain torque to athreshold torque level (creep torque) outside the lash region. Herein,the powertrain braking is applied before a brake pedal is actuallyapplied and may include a less than threshold amount of powertrainbraking applied to decelerate the vehicle at a slower rate to the creeptorque level. The torque is then maintained at the threshold torquelevel and a torque transition through the lash region is not initiated.That is, the first lash adjustment during a positive to negative torquetransition through the lash region is temporarily disabled. However, inother examples, the first lash adjustment is performed but at a latertime.

A rate of powertrain braking to the threshold torque level may beadjusted based on a rate of pedal displacement during the operatorfoot-off accelerator pedal event. For example, if the pedal is displacedat a lower rate (e.g., a lower closing rate of the pedal), then a lowerrate of powertrain braking (and/or lower amount of powertrain braking)may be applied. Further, the powertrain braking may be adjusted based onthe learned driving pattern of the operator, as discussed earlier.

Applying the powertrain braking responsive to the foot-off acceleratorpedal event when the vehicle is to be slowed via coasting includesswitching off fuel to the engine cylinders, and shifting thetransmission to neutral with the torque converter locked while theengine spins unfueled. In other words, the driveline is freewheeled byshifting the transmission into neutral, thereby decoupling the enginefrom the driveline downstream of the transmission clutches. In analternate example, the driveline may be freewheeled via a one-way clutchin the transmission that prevents the engine's friction from retardingthe vehicle's forwards motion when torque input to the one-way clutch bythe engine is less than torque on the wheel side of the one-way clutch.Optionally, one or more engine loads may also be varied. The powertraintorque may then be held at the creep torque level before drivelinetorque is increased from a creep torque level responsive to a demand forpositive torque, or decreased via a transition through the lash regionresponsive to a demand for negative torque. As elaborated below, atiming of each of the first and second lash adjustment during asubsequent transition through the lash region may be varied based onwhether and how soon an increase in torque demand is expected, as basedon the driver intent.

After adjusting the powertrain torque, method 300 proceeds to 324. At324, the routine may determine if positive driveline torque is expected.For example, it is determined if there is an indication that the drivermay reapply the accelerator pedal. The determination may be based on themonitored operator foot motion inside the foot-well region and/or basedon traffic patterns ahead of the vehicle. In one example, positivetorque is expected responsive to the driver moving their foot away fromthe brake pedal or towards the accelerator pedal (or hovering over theaccelerator pedal), and/or traffic clearing up outside the vehicleresulting in a smaller closing rate or larger clearance between thegiven vehicle and a leading vehicle. Details of determining expectedpositive torque based on driver foot motion and traffic movementsoutside the vehicle are discussed at FIG. 4. If positive powertraintorque is expected, the routine proceeds to 326.

At 326, the controller maintains the driveline torque at the thresholdtorque level outside the lash region (at the creep torque) until theaccelerator pedal is depressed at which time powertrain torque can beincreased from the creep torque level to the driver demanded level. As aresult, torque can be increased without the need for the drivelinepassing through the lash region. By maintaining a slight positive torquewhen positive driveline torque is imminently expected, drivability isimproved, time to torque is reduced, and lash adjustments are obviated.As a result, lash associated issues such as NVH are reduced.

If positive driveline torque is not expected, the routine proceeds to328 wherein the first lash adjustment is performed during a positive tonegative torque transition through the lash region while providingpowertrain braking to reduce the driveline torque to a decelerationtorque level. Thereafter, the second lash adjustment is performed duringa negative to positive torque transition through the lash region to acreep torque level. A duration between the first and second lashadjustment is extended and the second lash adjustment is performed laterso as to hold the driveline torque at the deceleration torque levellonger in anticipation of a demand for negative torque. If a brake pedalis applied while the driveline is at the deceleration torque level, thesecond lash adjustment can be avoided and negative torque can be appliedfrom the deceleration torque level. In this way, by providing a slightnegative torque when positive powertrain torque is not expectedsubsequently, the driveline is better prepared for converting kineticenergy to idle and FEAD power. Further, torque transitions within thelash zone may be reduced while improving vehicle response and reducingdriver discomfort. Method 300 then exits.

It will be appreciated that in addition to the powertrain brakingadjustments and the lash adjustments described above, the controller mayalso adjust an actuator (e.g., a first engine actuator) to take a firstaction responsive to the indication of driver intent to brake (such asthe driver intent to slow the vehicle via light braking, or theanticipated driver demand for negative torque). In comparison, thecontroller may adjust the actuator (e.g., the same first engineactuator) or another actuator (e.g., a second, different engineactuator) to take a second, different action from the first action,responsive to the indication of driver intent to coast (such as thedriver intent to slow the vehicle via coasting, or the anticipateddriver demand for positive torque).

As an example, responsive to the driver intent to brake, an ACcompressor may be actuated to increase an engine load, while responsiveto the driver intent to coast, the AC compressor may be deactivated toreduce the engine load. In yet another example, an engine transmissionmay be engaged in gear and the torque converter may be locked.Consequently, powertrain braking may be increased by downshifting thetransmission gear, and increasing the output power of an alternator (tothereby increase the alternator load on the engine). Further, powertrainbraking may be increased by engaging a clutch of an AC compressor (toincrease the AC compressor load on the engine) and increasing thedisplacement of the transmission clutch to provided higher levels ofbraking.

Referring to FIG. 4, an example method 400 is shown for determiningdriver intent based on input from various sensors such as operator footmotion inside a foot-well captured by a foot camera and traffic patternsincluding closing rate to a leading vehicle as determined by a rangesensor. The method of FIG. 4 may be used in conjunction with the methodof FIG. 3. For example, method 400 may be performed at steps 310, 317,and 324 of method 300. The method of FIG. 4 may be stored as executableinstructions in non-transitory memory of controller 12 shown in FIGS.1-2.

At 402, the method includes receiving situational information from oneor more sensors, such as information on operator foot position from afoot-well region sensor or camera installed inside an operator foot-wellregion of the vehicle (such as foot camera 280 at FIG. 1) andinformation on traffic movements outside the vehicle from a range sensor(such as sensor 290 of FIG. 1). The foot camera monitors operator footposition with respect to each of an accelerator and a brake pedal, andrelays foot position information to a controller. This includesmonitoring a location and motion of the foot immediately after anaccelerator pedal tip-out event or a brake pedal tip-out event.

The range sensor (which may be configured as a traffic camera) monitorstraffic movements outside the vehicle and relays the traffic informationto the controller. In one example, the sensor may monitor if trafficoutside the vehicle is slowing down or clearing by sensing a gap orclearance between the given vehicle and a vehicle immediately ahead ofit (that is, a closing rate to a leading vehicle). If the closing rateof the given vehicle is increasing, or the gap between the given vehicleand a leading vehicle immediately ahead of it is decreasing, it may bedetermined that traffic outside the current vehicle is slowing down, anddriver intent to slow vehicle down via powertrain braking may beinferred. Alternatively, if the closing rate of the given vehicle isdecreasing, or the gap between the given vehicle and the leading vehicleimmediately ahead of it is increasing, it may be determined that thetraffic outside the vehicle is clearing, and it may be inferred that thedriver intends to slow the vehicle down via coasting. After receivingthe situation information, the routine moves to both 404 and 414. Insome examples, after receiving information on operator foot positionwith respect to accelerator and brake pedal, the routine proceeds to404. Likewise, after receiving information on traffic motion, method 400proceeds to 414.

At 404, the routine may determine if the operator foot is off the gopedal event for a long duration. In one example, the controller maydetermine if the vehicle operator's foot moves to towards the brakepedal, and if so, further determine for how long the driver's foothovers over the brake pedal (following a foot-off go pedal event). Ifthe driver's foot moves towards and hovers over the brake pedal for along duration (such as longer than a threshold) after releasing theaccelerator pedal, then it may be inferred that driver intends to brake.Accordingly at 406, the method includes inferring that negativepowertrain torque is expected responsive to the driver's foot hoveringover the brake pedal for a long duration.

Returning to 404, if the foot off go pedal event is not for a longduration, then at 408, the routine includes determining if the foot offgo pedal is present for a short duration. In one example, if thedriver's foot does not move towards the brake pedal and instead hoversover the accelerator pedal, or hovers over the brake pedal for a shortduration (such as shorter than a threshold) after releasing theaccelerator pedal, it may be inferred that the driver intends to slowthe vehicle down via coasting. Accordingly at 410, the method includesinferring that positive powertrain torque is expected responsive to thedriver's foot hovering over the brake pedal for a short duration.

If a foot-off go pedal event is not present, the routine returns to 402to continue monitoring foot motion inside the foot well and trafficmovements outside the vehicle.

From each of 406 and 410, after determining the expected drivelinetorque based on foot off pedal event and duration of the event, theroutine proceeds to 412 to record and store information regarding theexpected driveline torque in the controller's memory. In addition, at424, based on operator foot motion at the foot-off go pedal event, anoperator driving pattern is learned and/or updated. The method thenexits.

Returning to 402, after determining traffic movements outside thevehicle, method 400 proceeds to 414. At 414, the routine may determineif traffic is slowing down outside the vehicle. In one example, trafficmay be slowing down when the vehicle clearance is decreasing or closingrate is increasing. If the answer is YES, the routine proceeds to 416.At 416, the method may infer that negative driveline torque is expectedresponsive to traffic slowing down outside the vehicle. For example, itmay be expected that the driver will imminently apply vehicle brakes toslow down the vehicle.

Returning to 414, if the traffic outside the vehicle is not slowingdown, the routine proceeds to 418. At 418, the routine may determine iftraffic outside the vehicle is clearing. In one example, traffic may beclearing when the vehicle clearance is increasing or closing rate isdecreasing. If the answer is YES, method 400 proceeds to 420. At 420,the method may infer that positive driveline torque is expectedresponsive to traffic clearing outside the vehicle. For example, it maybe inferred that the driver is coasting.

If the traffic outside the vehicle is not clearing or slowing down, theroutine returns to 402 to continue monitoring foot motion inside thefoot well and traffic movements outside the vehicle.

From each of 416 and 420, after determining the expected drivelinetorque based on vehicle clearance and closing rates, the routineproceeds to 422 to record and store information regarding the expecteddriveline torque in the controller's memory. In addition, at 424, basedon operator foot motion at the foot-off go pedal event, an operatordriving pattern is learned and/or updated. The method then exits. In oneexample, lash adjustments in a vehicle driveline may be varied based oninput from a first camera scanning a foot-well region of the vehicle,and input from a second camera scanning a region in front of thevehicle. Specifically, inputs from the first and second camera mayindicate and differentiate driver intent to brake or coast, enabling atiming of lash adjustments to be varied. In this way, lash adjustmentsmay be adjusted based on driver intent in order to reduce drivelinetorque variations and reduce frequency of unnecessary torque transitionsthrough a lash region.

Referring to FIG. 5, an example graphical output 500 is shown foradjusting lash in a vehicle driveline based on situational information,such as driver foot motion and traffic movements outside the vehicle.

The first graph represents change in vehicle speed over time at plot501. The second graph represents accelerator pedal position(Accelerator_PP) versus time at plot 502. The vertical axis representsthe accelerator pedal position and accelerator pedal is fully depressedin the direction of the vertical axis. The third graph represents brakepedal position (Brake_PP) versus time at plot 504. The vertical axisrepresents the brake pedal position and brake pedal is fully depressedin the direction of the vertical axis. The fourth graph representspowertrain torque versus time at plot 506. The vertical axis representsthe powertrain torque and powertrain torque increases in the directionof the vertical axis. Powertrain torque values above zero torque(represented by a long dashed horizontal line) represent positive torquewhile powertrain torque values below zero torque represent negativetorque (or brake torque). A lash zone 507, defined as region wheretorque reversals occur, is demarcated by a band of positive and negativetorque around the zero torque value, depicted herein via small dashedhorizontal lines. The fifth graph represents a torque converter clutch(TCC) operating state (locked or unlocked) versus time at plot 508. Thesixth graph represents a clearance in the vehicle's path. The clearanceis representative of a gap between the given vehicle and a leadingvehicle ahead of it and may be inferred via a range sensor. It will beappreciated that while the clearance is depicted as a distance, inalternate examples it may be depicted as a time to impact. Verticalmarkers at times T0-T13 represent time of interest during the sequence.In all the plots discussed below, the horizontal axis represents timeand time increases from the left side of each plot to the right side ofeach plot.

At T0, a vehicle is moving and the accelerator pedal (502) is maintainedat a steady position (e.g., a middle level), with the transmission in aforward gear (such as a first gear) and torque converter (508) locked toensure better fuel economy and to transmit positive powertrain torque(506). At T1, a driver releases the accelerator pedal until it iseventually fully released (that is, the driver takes their foot off theaccelerator pedal). Herein, the accelerator pedal is released by theoperator at a slower rate. The vehicle speed begins to decrease inresponse to the reduction in torque request following the foot-offaccelerator pedal event. At this time, as estimated by the range sensor,a clearance between the given vehicle and a vehicle ahead of it islarger (such as due to traffic clearing out) such that at theaccelerator pedal tip-out event, it may be anticipated that the driverintends to slow the vehicle down via coasting. Since brake applicationis not expected, at T1, a smaller rate of driveline braking is providedby deactivating the engine so that it does not combust fuel and air, andshifting the transmission to neutral while the TCC remains locked. Whilethe vehicle driveline freewheels, a smaller rate of driveline braking isapplied to reduce powertrain torque to a first (slightly positive)threshold torque 520 (creep torque) outside lash zone 507 in view of theslower rate of pedal displacement during the foot-off pedal event. Inthis way, engine torque may be reduced to a threshold torque outside alash zone in response to a first operator foot-off accelerator pedalevent. Subsequently, the powertrain torque may be maintained at thethreshold torque until a subsequent operator foot-on accelerator pedalevent. Herein, a lash adjustment is not performed in anticipation ofpositive torque demand. As the vehicle speed decreases, the clearanceahead of the vehicle may increase.

At T2, the accelerator pedal may be fully released and the vehicle speedmay reduce further to a lower speed less than a threshold speed, and thetorque converter clutch may remain locked for better fuel economy. Thevehicle may remain in a neutral idle state with powertrain torque at thecreep torque level 520 until a further increase in torque demand isreceived.

At T3, the driver applies the accelerator pedal to increase vehiclespeed. Herein, the accelerator pedal is applied while the vehicle iscoasting and before the vehicle speed has been reduced to a zero speed.In one example, the accelerator pedal is released when the vehicle is at55 mph and the accelerator pedal is reapplied when the vehicle speed hasbeen reduced to 50-52 mph. In response to the increased torque demand,the engine is reactivated (and combustion of air and fuel is resumed)and the transmission is shifted into a forward gear (e.g., a firstgear). The engine is reactivated and the transmission is placed in gearto meet the non-zero torque demand requested by the foot-on acceleratorpedal event. Further, the torque converter clutch may remain locked andthe powertrain torque may increase. As the vehicle speed increases, theclearance ahead of the vehicle may decrease. By enabling the drivelinetorque to be held at the creep torque raised therefrom responsive to theincrease in torque demand, a time to torque is reduced and unnecessarylash transitions are obviated.

At T4, the driver releases the accelerator pedal at a higher rate ofdisplacement until it is eventually fully released (that is, the drivertakes their foot off the accelerator pedal faster). The vehicle speedbegins to decrease in response to the reduction in torque requestfollowing the foot-off accelerator pedal event. In this case, thevehicle speed may initially decrease at a rate that is proportional tothe higher rate of displacement. In particular, the vehicle speeddecreases following the foot-off accelerator pedal event at a fasterrate than the decrease in vehicle speed following the foot-offaccelerator pedal event at T1 where the rate of displacement was lower.However, the powertrain braking and rate of drop in vehicle speed at T4is smaller than the powertrain braking and rate of drop in vehicle speedachieved when the brake pedal is applied (at T5). At this time, asestimated by the range sensor, a clearance between the given vehicle anda vehicle ahead of it is smaller (such as due to traffic slowing down)such that at the accelerator pedal tip-out event, it may be anticipatedthat the driver is likely to brake imminently. Responsive to the highrate of pedal displacement, a larger driveline braking is applied at T4.In particular, the engine is deactivated, the torque converter clutchmay remain locked, and the transmission is held in gear so that enginebraking torque can be used to counter wheel torque provided from thevehicle wheels to the driveline. The driveline braking is used to reducepowertrain torque to the zero torque level where it is held until thevehicle reaches a speed lower than a threshold speed. Then, with thetorque converter clutch locked, further powertrain braking is used toreduce the powertrain torque from the zero torque to a second (slightlynegative) threshold torque 530 (herein referred to as decelerationtorque) outside the lash zone 507 in anticipation for more negativepowertrain torque. A first lash adjustment is applied as the powertraintorque undergoes a positive to negative torque transition while movingthrough the lash zone.

To prepare the driveline for a subsequent increase in torque demand, thepowertrain torque is required to be transitioned from second thresholdtorque 530 to first threshold torque 520 with a second lash adjustmentapplied as the powertrain torque undergoes a negative to positive torquetransition while moving through the lash zone. However herein, inanticipation of driver intent to brake (due to the smaller clearance),the second lash adjustment and the transition through the lash zone isdelayed. Thus, the powertrain is held at the deceleration torque levellonger in anticipation of negative torque demand.

At T5, the driver may apply the brake pedal to request powertrainbraking and the torque converter may be unlocked. At this time, thevehicle speed may decrease at a faster rate than previously achievedwhen powertrain braking is applied at foot-off accelerator pedal (T4).For example, the vehicle speed may initially decrease from 50 mph to 15mph, and then decrease further to zero speed. The engine may continuerunning while the vehicle is stopped. Since the second lash adjustmenthas been delayed, the controller is able to rapidly provide the negativetorque demand from the deceleration torque level. Thereafter, once thebrake pedal is released at T6, the driveline is returned to thedeceleration torque level and the deceleration torque may be maintained.Due to the braking, the vehicle clearance may increase and may be largerby T6. For example, traffic outside the vehicle may be clearing. Thevehicle controller may therefor infer a driver intent to acceleratebased on the larger clearance between vehicle and a leading vehicle.Therefore between T6 and T7, powertrain torque may be increased from thesecond threshold torque to the first threshold torque while performinglash adjustments when transitioning through the lash zone inanticipation that the driver may request more positive powertrain torquesubsequently. After T7, the creep torque is held until positive torqueis requested.

Herein, in anticipation of a driver intent to request positive torque(or to coast) in view of the larger clearance, the lash adjustment andlash zone transition is performed earlier. The earlier transition to thecreep torque enables the positive torque to be rapidly provided when itis eventually demanded, improving drivability. It will be appreciatedthat if the clearance was smaller and a driver intent to requestnegative torque (or further braking) was anticipated, the lashadjustment and lash zone transition may have been performed later (asindicated by dashed segment 505). The later transition to the creeptorque enables the negative torque to be rapidly provided when it iseventually demanded, improving drivability. At T8, the driver may applythe accelerator pedal and the torque converter clutch may remainunlocked to launch vehicle from zero speed to a higher speed. Forexample, the vehicle may be launched from zero speed to 15 mph. BetweenT8 and T9, as the accelerator pedal is depressed, the torque converterclutch is locked, transmission is engaged in gear and powertrain torquemay increase. The vehicle speed correspondingly increases.

At T10, the accelerator pedal is released and the torque converter maybe unlocked, however due to the larger clearance, vehicle coasting isexpected and braking is not expected. Therefore at T10, a smaller rateof driveline braking is provided to reduce powertrain torque to thefirst threshold torque 520 outside lash zone 507 and maintain it there.Subsequently, the vehicle speed may decrease gradually. For example, thevehicle speed may decrease from 15 mph to 10 mph. However, at T11, theoperator unexpectedly applies the brake pedal. Responsive to the brakepedal application, the powertrain torque is transitioned through thelash zone and then negative torque is applied. Consequently, the vehiclespeed may decrease further. In one example, the vehicle speed maydecrease from 10 mph to zero speed. The engine may continue runningwhile the vehicle is stopped. At T12, once the brake pedal is released,the powertrain negative torque is returned to second threshold torque530. At T13, the powertrain torque is once again transitioned throughthe lash zone and held at first threshold torque 520 in anticipation ofpositive torque due to the larger clearance. At T14, the acceleratorpedal is applied and positive torque is provided. The torque convertermay remain unlocked to launch vehicle from zero speed to a higher speedsuch as 10 mph, for example. After T14, the vehicle speed may increasefurther and the torque converter may be locked to transmit positivetorque and provide better fuel economy.

In this way, responsive to a first operator foot-off accelerator pedalevent, an engine controller may reduce engine torque to a thresholdtorque outside a lash region, and maintain the engine torque at thethreshold torque until a subsequent operator foot-on accelerator pedalevent. In comparison, in response to a second operator foot-offaccelerator pedal event, the controller may reduce engine torque to thethreshold torque outside a lash region, then transition through the lashregion via a first lash adjustment followed by transitioning through thelash region via a second lash adjustment, a duration between the firstand the second lash adjustment adjusted based on inferred driver intentto brake differentiated from driver intent to coast. Herein, during eachof the first and second events, a rate of reducing the engine torque tothe threshold torque outside the lash region is based on a rate of pedaldisplacement, the rate of reducing increased as the rate of pedaldisplacement increases. Reducing engine torque includes reducing enginetorque via powertrain braking. Responsive to the second operatorfoot-off accelerator pedal event, the duration between the first and thesecond lash adjustment may be decreased when the inferred driver intentis to coast, and the duration may be increased when the inferred driverintent is to brake. Herein, the inferred driver intent is based on eachof operator foot motion and vehicle clearance following the secondoperator foot-off accelerator pedal event, the operator foot motioninferred via a sensor coupled to a vehicle operator foot-well region,the vehicle clearance inferred via a vehicle gap sensor. The inferreddriver intent may be further based on a learned operator drivingpattern, the learned driving pattern including one or more of anaccelerator pedal patterns, a brake pedal pattern, a preference forvehicle performance, and a preference for engine fuel economy. Further,in response to a brake pedal event following the first operator foot-offaccelerator pedal event, the engine controller may transition thedriveline torque through the lash region from the threshold torque viathe first lash adjustment followed by transitioning through the lashregion via the second lash adjustment, the duration between the firstand the second lash adjustment adjusted based on a braking demand duringthe brake pedal event. Herein, the first lash adjustment is performedduring a positive-to-negative torque reversal through the lash region,while the second lash adjustment is performed during anegative-to-positive torque reversal through the lash region.

In this way, unnecessary torque transitions through a lash region arereduced. By maintaining at least a creep torque responsive to aninferred driver intent to coast following a foot-off accelerator pedalevent, a subsequent positive torque demand can be rapidly met, improvingtime to torque. Likewise, by adjusting a time when a torque transitionthrough the lash region is initiated based on the driver intent,drivability is improved. Specifically, by initiating a transitionthrough the lash region to the creep torque earlier responsive to theinferred driver intent to coast following a foot-off accelerator pedalevent, the positive torque demand can be met rapidly. In comparison, byinitiating the transition through the lash region to the creep torquelater responsive to a inferred driver intent to brake following afoot-off accelerator pedal event, a negative torque demand can be metrapidly, such as from a deceleration torque level. By adjusting atransition through the lash zone, fuel losses and NVH issues associatedwith lash adjustments are reduced. Overall, vehicle performance andcomponent life is improved.

In one example, a method for an engine in a vehicle comprises: inresponse to an operator foot-off accelerator pedal event, distinguishingbetween a driver intent to brake or coast based on one or more ofoperator foot motion inside the vehicle and traffic pattern outside thevehicle; and varying lash adjustments during torque transition through alash region following the operator foot-off accelerator pedal eventbased on the driver intent. In the preceding example, additionally oroptionally, the lash adjustments include a first lash adjustment duringa positive-to-negative torque transition through the lash region andvarying a second lash adjustment during a negative-to-positive torquetransition through the lash region. In any or all of the precedingexamples, additionally or optionally, the varying includes, when thedriver intent includes coasting, reducing engine torque to a thresholdtorque level outside the lash region, and disabling each of the firstand second lash adjustment, where the lash region is based on torqueconverter input and output speeds of a fully unlocked torque converter.In any or all of the preceding examples, additionally or optionally, thevarying includes, initiating the first lash adjustment at a timing basedon a rate pedal displacement during the operator foot-off acceleratorpedal event, and then initiating the second lash adjustment earlierduring the torque transition when the driver intent includes coasting,and initiating the second lash adjustment later during the torquetransition when the driver intent includes braking. In any or all of thepreceding examples, additionally or optionally, the varying is furtherbased on an operator driving pattern, the operator driving patternincluding a preference for performance relative to a preference for fueleconomy.

Further, in any or all of the preceding examples, additionally oroptionally, the varying includes initiating each of the first lashadjustment and the second lash adjustment earlier when the operatordriving pattern includes a preference for performance over fuel economy,and initiating each of the first lash adjustment and the second lashadjustment later when the operator driving pattern includes a preferencefor fuel economy over performance. In any or all of the precedingexamples, additionally or optionally, the distinguishing includesindicating driver intent to brake responsive to operator foot motiontowards a brake pedal and indicating driver intent to coast responsiveto operator foot motion near an accelerator pedal. In any or all of thepreceding examples, additionally or optionally, the distinguishingincludes indicating driver intent to brake responsive to traffic patternindicative of smaller clearance ahead of vehicle, and indicating driverintent to coast responsive to traffic pattern indicative of largerclearance ahead of vehicle. In any or all of the preceding examples,additionally or optionally, the operator foot motion inside the vehicleis based on input from a camera scanning a foot-well region of thevehicle, and wherein the traffic pattern outside the vehicle is based oninput from a camera scanning a region in front of the vehicle.

In another example, a method for an engine coupled to a vehicle maycomprise: in response to a first operator foot-off accelerator pedalevent, reducing engine torque to a threshold torque outside a lashregion, and maintaining the engine torque at the threshold torque untila subsequent operator foot-on accelerator pedal event; and in responseto a second operator foot-off accelerator pedal event, reducing enginetorque to the threshold torque outside a lash region, then transitioningthrough the lash region via a first lash adjustment followed bytransitioning through the lash region via a second lash adjustment, aduration between the first and the second lash adjustment adjusted basedon inferred driver intent to brake differentiated from driver intent tocoast. In the preceding example, additionally or optionally comprise,during each of the first and second events, a rate of reducing theengine torque to the threshold torque outside the lash region is basedon a rate of pedal displacement, the rate of reducing increased as therate of pedal displacement increases. In any or all of the precedingexamples, additionally or optionally, reducing engine torque includesreducing engine torque via powertrain braking. In any or all of thepreceding examples, additionally or optionally, responsive to the secondoperator foot-off accelerator pedal event, the duration between thefirst and the second lash adjustment is decreased when the inferreddriver intent is to coast, and the duration is increased when theinferred driver intent is to brake.

Further yet, in any or all of the preceding examples, additionally oroptionally, the inferred driver intent is based on each of operator footmotion and vehicle clearance following the second operator foot-offaccelerator pedal event, the operator foot motion inferred via a sensorcoupled to a vehicle operator foot-well region, the vehicle clearanceinferred via a vehicle gap sensor. In any or all of the precedingexamples, additionally or optionally, the inferred driver intent isfurther based on a learned operator driving pattern, the learned drivingpattern including one or more of an accelerator pedal patterns, a brakepedal pattern, a preference for vehicle performance, and a preferencefor engine fuel economy. Any or all of the preceding examples, mayadditionally or optionally, further comprise, in response to a brakepedal event following the first operator foot-off accelerator pedalevent, transitioning through the lash region from the threshold torquevia the first lash adjustment followed by transitioning through the lashregion via the second lash adjustment, the duration between the firstand the second lash adjustment adjusted based on a braking demand duringthe brake pedal event. In any or all of the preceding examples,additionally or optionally, the first lash adjustment is performedduring a positive-to-negative torque reversal through the lash region,and wherein the second lash adjustment is performed during anegative-to-positive torque reversal through the lash region.

Another example vehicle system comprises: an operator foot-well regionincluding an accelerator pedal, a brake pedal, and a foot-well sensor; asensor coupled to the vehicle system for estimating a gap between thevehicle system and a leading vehicle; an engine including a fuelinjector and an intake throttle valve; and a controller withcomputer-readable instructions stored on non-transitory memory for: inresponse to a foot-off accelerator pedal event, applying a firstpowertrain brake torque to reduce engine torque to a threshold torqueabove a lash region via adjustments to a duty cycle of the fuel injectorand an opening of the intake throttle valve; inferring a driver intentto coast or brake based on one or more of the traffic sensor and thefoot-well sensor; and selectively performing a lash adjustment throughthe lash region based on the inferred driver intent. In any or all ofthe preceding examples, additionally or optionally, the selectivelyperforming the lash adjustment includes: performing the lash adjustmentwhen the inferred driver intent includes braking; and not performing thelash adjustment when the inferred driver intent includes coasting. Inany or all of the preceding examples, additionally or optionally, theselectively performing the lash adjustment further includes: initiatingthe lash adjustment through the lash region earlier when the inferreddriver intent includes coasting; and initiating the lash adjustmentthrough the lash region later when the inferred driver intent includesbraking.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for an engine of a vehicle,comprising: following an operator foot-off accelerator pedal event,distinguishing between a driver intent to brake or coast based on eachof operator foot motion inside the vehicle and traffic pattern outsidethe vehicle; and varying a lash adjustment during torque transitionthrough a lash region based on the driver intent, wherein the varyingincludes varying an initiation of the lash adjustment through the lashregion based on the driver intent, the lash adjustment initiated earlierwhen the driver intent includes coasting, the lash adjustment initiatedlater when the driver intent includes braking.
 2. The method of claim 1,wherein the varying further includes varying lash in a vehicle drivelineby adjusting an amount of positive or negative torque applied to thedriveline.
 3. The method of claim 1, wherein the varying furtherincludes varying an amount and rate of powertrain braking applied on adriveline following the foot-off accelerator pedal event based on thedriver intent.
 4. The method of claim 3, wherein the rate of powertrainbraking is further based on a rate of pedal displacement during thefoot-off accelerator pedal event.
 5. The method of 3, wherein thevarying includes: when the driver intent includes coasting, applyingpowertrain braking to reduce a drivetrain torque to a level outside thelash region of a powertrain of the vehicle; and then maintaining thedrivetrain torque at the level until a subsequent operator foot-onaccelerator pedal event.
 6. The method of claim 1, further comprising:responsive to the driver intent to brake, increasing an engine load viaactuation of an air conditioning (AC) compressor; and responsive to thedriver intent to coast, decreasing the engine load by deactivating theAC compressor.
 7. The method of claim 2, wherein the lash region isbased on each of an input speed and an output speed of a fully unlockedtorque converter coupled in the driveline.
 8. The method of claim 2,wherein the lash region includes a band of positive and negativedriveline torque on either side of a zero driveline torque.
 9. Themethod of claim 1, wherein the varying further includes: when the driverintent is coasting, applying powertrain braking to reduce drivelinetorque to a positive torque outside the lash region, then maintainingthe driveline torque outside the lash region until an operator foot-onpedal event; and when the driver intent is braking, applying powertrainbraking to reduce the driveline torque to a negative torque outside thelash region when an accelerator pedal is released, and then applyingfurther braking torque to decrease vehicle speed when a brake pedal isapplied.
 10. A method for an engine coupled to a vehicle, comprising:responsive to a first operator foot-off accelerator pedal event,reducing engine torque to a threshold torque outside a lash region, andmaintaining the engine torque at the threshold torque until a subsequentoperator foot-on accelerator pedal event; responsive to a secondoperator foot-off accelerator pedal event, reducing engine torque to athreshold positive torque outside the lash region, then transitioningthrough the lash region at a slower rate to reduce engine torque to athreshold negative torque outside the lash region; and responsive to athird operator foot-off accelerator pedal event, reducing engine torqueto the threshold positive torque outside the lash region, thentransitioning through the lash region at a faster rate to reduce enginetorque to the threshold negative torque outside the lash region.
 11. Themethod of claim 10, further comprising, responsive to the second andthird operator foot-off accelerator pedal events, further transitioningthrough the lash region from the threshold negative torque towards thethreshold positive torque, a duration between a positive to negativetransition and a negative to positive transition adjusted based oninferred driver intent to brake differentiated from inferred driverintent to coast.
 12. The method of claim 11, wherein the duration isdecreased when the inferred driver intent is to coast, and the durationis increased when the inferred driver intent is to brake.
 13. The methodof claim 10, wherein during each of the first, second, and thirdoperator foot-off accelerator pedal events, a rate of reducing theengine torque to the threshold positive torque outside the lash regionis based on a rate of accelerator pedal displacement, the engine torquereduced at a faster rate as the rate of accelerator pedal displacementincreases.
 14. The method of claim 10, wherein reducing engine torqueincludes reducing engine torque via powertrain braking.
 15. The methodof claim 11, further comprising inferring the driver intent to brake orcoast based on each of operator foot motion and vehicle clearancefollowing each foot-off accelerator pedal event, the operator footmotion inferred via a sensor coupled to a vehicle operator foot-wellregion, the vehicle clearance inferred via a vehicle gap sensor.
 16. Themethod of claim 15, wherein the driver intent is further inferred basedon a learned operator driving pattern, the learned driving patternincluding one or more of accelerator pedal patterns, brake pedalpatterns, and an indicated preference for vehicle performance relativeto engine fuel economy.
 17. A method for an engine of a vehicle,comprising: following an operator foot-off accelerator pedal event,distinguishing between a driver intent to brake or coast based on eachof operator foot motion inside the vehicle and traffic pattern outsidethe vehicle; and varying a lash adjustment during torque transitionthrough a lash region based on the driver intent, including varying anamount and rate of powertrain braking applied on a driveline followingthe foot-off accelerator pedal event based on the driver intent.
 18. Themethod of claim 17, wherein the rate of powertrain braking is furtherbased on a rate of pedal displacement during the foot-off acceleratorpedal event.
 19. The method of 17, wherein the varying includes: whenthe driver intent includes coasting, applying powertrain braking toreduce a drivetrain torque to a level outside the lash region of apowertrain of the vehicle; and then maintaining the drivetrain torque atthe level until a subsequent operator foot-on accelerator pedal event.